The threat of an epidemic of Salmonella fevers is constant in the world as shown by epidemiological reports and the seriousness of the spread of epidemics due to various Salmonellas which have evolved to have an increased resistance to antibiotics.
It has been known for a long time that there is no parallelism between the proportion of anti-O, anti-H or anti Vi agglutinant antibodies, shown in the case of Salmonellosis, and the degree of acquired immunity to these bacteria. The only valid criterion of vaccinal effectiveness is the protection of the individual or animal from a similar infectious bacterium.
Several types of vaccines have already been proposed; however, these vaccines exhibit various drawbacks and dangers. Thus, injectable inactive vaccines (TAB) are not without danger for persons who receive them for a relative effectiveness in relation to a test dose not exceeding 10.sup.5 pathogenic bacteria. On the other hand, oral vaccines, and more particularly those that contain live bacteria, prove more effective but their use still poses a certain number of problems of a practical order inherent in the difficulties of preservation and of a psychological order.
It has been considered that the use of protective purified fractions extracted from bacteria would satisfactorily solve the problem of vaccination against Salmonellas. And knowing that all bacteria can be considered as made up of antigen mosaics, the outside membrane of the ectoplasmatic wall appearing, in Salmonellas (gram negative) as the anatomic support of the vaccinating antigent, an effort was made to find a means of preferential extraction of this vaccinating antigen.
Various works, particularly those of O. Westphal et al of the Max Planck Institute, published particularly in Zentralbl. Bacteriol; Mikrobiol. Hyg. 1 ABt Orig. a. med. mikrobiol. infektionskr. Parasitol 248 (1), 1980, 64-80, showed the use of guanidine thiocyanate, urea and veronal buffer in the extraction of molecules with a protein base, in particular from gram negative bacteria such as Salmonella typhimurium and S. minnesota and mutant forms 5 R.